Report on the Bacteriology of Water. 369 



I also, at the end of the experiment on October 12, cautiously 

 emptied each of the water tubes, and drained it until only a drop 

 remained, and then filled up with sterile broth. After sixteen hours 

 the dark tube was distinctly turbid, whereas no trace of turbidity 

 appeared in the insolated one till after forty-eight hours. Both were 

 equally turbid on the fourth day. 



Of course I recognise that this last result, and that obtained with 

 the stab-cultures, is attributable to the numbers of still living germs 

 added to the gelatine and broth respectively, and the experiments 

 only go to prove once more, but in a very decisive manner, what 

 mortality the sun had occasioned in the exposed tube for we must 

 remember, each tube contained practically the same enormous num- 

 bers at the start. 



XXI. 



On October 6 a loopful of a markedly liquefying form, marked 

 in my notes as colony 0, was placed in each of two tubes of broth, and 

 placed in the sun from 9 A.M. to 4 P.M. One tube was exposed over a 

 mirror, the other side by side, but wrapped in foil and black paper. 

 The sun shone brightly from 9 to 1, and then was obscured by clouds. 



At 4 P.M. a plate and a stab-culture from each tube were made, and 

 the tubes put at 20 to 22 C. in the dark incubator. The plate and 

 stab-cultures were put at 15 C. in the dark. 



Taking the broth tubes first. Both were already turbid in eighteen 

 hours, more densely so after forty hours, so that no difference between 

 them could be detected. 



Of the stab-cultures, that from the dark tube had taken in forty 

 hours, while the one from the lighted tube showed no signs. 



In sixty-four hours the non-illuminated culture had developed a 

 thistle-head liquefaction funnel, whereas no trace was visible in the 

 other. In eighty-eight hours the liquefaction had proceeded rapidly 

 in the former tube ; only one feeble colony was visible in the tube 

 from the insolated broth. In the course of a week or so r o further 

 difference could be made out. 



With regard to the plates. That from the insolated tube showed 

 no trace until sixty-four hours had passed, when two or three colonies 

 g- to f mm. diameter were seen. In eighty-six hours these were 

 somewhat like young anthrax colonies, each with a slight depression. 

 On the sixth day liquefaction of the gelatine was slowly evincing 

 itself. 



The plate from the dark tube showed evident colonies, f to ^, and 

 even 1 mm. in diameter, in forty hours ; and in sixty-four hours they 

 averaged 2 to 5 mm. in diameter, and were liquefying rapidly. 

 These circular colonies were less rapid than those of colony /3 at tho 



